Liquid composites molding is a low cost and high efficiency process of composites manufacturing.The presented work is based on Richard’s equation and a contour function to predict the pressure field and resinflow front tracking at transient situation of VARTM (vacuum assisted resin transfer molding) process. Finite element method (FEM) is applied to carry out the numerical simulation realized by COMSOL Multiphysics software. A parameter named infusion ratio λ to compare the results of numerical simulation and the experiment. Good matching of the results is achieved to prove the credibility of this method.